1. Technical Field
This invention relates generally to wood reducing apparatus of the type used to reduce trees, limbs, and other wood debris into chips or grindings by advancing the material into the path of a rotating chipping or grinding drum or disc, and more particularly to automated feed systems for such wood reducers which engage and advance the material for chipping or grinding.
2. Related Art
There are various devices known in the art used for reducing trees, tree limbs, and other scrap wood products such as wood pallets and the like into chips or grindings. The material is introduced into a feed chute and advanced against a rotating reducing drum or wheel driven within a chamber downstream of the feed chute, which carries a series of spaced knives or teeth that cut or shred the material into chips or grindings.
Such apparatus are typically equipped with a power driven feed system located in a throat of the feed chute upstream of the rotating reducing drum or wheel which operates to engage and advance the material toward the reducer. One such feed system 11 employed in various prior art wood chipping apparatus 13 (portable and stationary equipment) manufactured by the assignee of the present invention is illustrated in FIGS. 1 and 2, and includes a set of opposed feed drums 15, 17 which are mounted in the throat 19 of the apparatus 13. The drums 15, 17 are counter rotating and power driven by hydraulic motors which operate to positively drive the upper and lower drums 15, 17 in opposite directions away from the feed chute for drawing the wood feed material into a feed gap 21 between the upper and lower feed drums 15, 17. The upper feed drum 15 is mounted on a swing arm 23 which straddles the chipping chamber and is pivoted to the frame 25 of the apparatus 13 by pivot mount 27, enabling the upper feed drum 15 to be displaced relative to the lower feed drum 17 in order to vary the gap 21 between the drums 15, 17 to enable feed material of varying diameter and bulk to be fed to the gap 21 between the drums 15, 17. The enlarged fragmentary view of FIG. 2 shows the feed drum 15 in a fully lowered position (solid lines) and a fully-raised position (broken chain lines). Tension springs 29 (only one shown) are connected to the frame 25 of the apparatus 13 at their lower end on opposite sides of the chipping chamber and are coupled to the movable swing arm 23 at their upper ends outwardly of the pivot mount 27. The springs 29 act to urge the swing arm 23 downwardly, and thus constantly bias the upper feed drum 15 to the fully lowered solid line position.
As feed material is presented to the gap 21, the upper feed drum 15 rides on top of the material and thus widens the gap 21 to enable the material to pass between the drums 15, 17. The upward movement of the feed drum 15 is counteracted by the downward tension force exerted by the springs 29. The tension springs 29 thus apply a certain compression load on the material being fed into the gap 21. Under most conditions, the force applied by the tension springs 29 is sufficient to grip the material firmly enough to draw the material into the rotating chipper mechanism 31. However, due to the inherent spring constant characteristic of a tension spring 29, the closing compression force exerted by the springs 29 varies with the position of the swing arm 23, such that the tension springs 29 provide far less compression force when the upper feed drum 15 is at or near the fully lowered solid line position and increases when the gap 21 is opened through movement of the feed drum 15 toward the broken line raised position of FIG. 2. Consequently, when the material fed to the gap 21 is relatively small, such as small tree branches and the like, the tension springs 29 may not provide sufficient compression force to grip and draw the material into the rotating chipper 31 without slipping.
A pair of hydraulic cylinders 33 are connected at their lower end to the frame 25 on opposite sides of the chipping chamber (only one shown) and at their upper end to the swing arm 23 outwardly of the pivot mount 27. The cylinders 33 have a set of upper and lower feed/return lines 35, 37 which communicate with the upper and lower ends of the cylinders 33 and are coupled to a manually operable valve bank 39. The valve bank operates manually via a lever 41 to position the cylinders 33 in either a neutral position in which hydraulic fluid is permitted to flow freely into and out of both ends of the cylinders such that the cylinders 33 do not exert any substantial resistance to the raising or lowering of the swing arm 33, but go along for the ride, or hydraulic fluid under pressure may be pumped into the lower end of the cylinders 33 to manually raise the upper feed drum 15 in the event that the incoming feed material is awkwardly shaped or otherwise the upper feed drum 15 requires manual assistance from the hydraulic cylinders 33 to raise the feed drum 15 high enough to climb on top of the feed material, or to manually feed pressurized hydraulic fluid into the upper end of the cylinders 33 to urge the upper feed drum 15 downwardly. In normal operation, the cylinders 33 are maintained in the neutral position and thus do not play any role in applying a compressive gripping force to the incoming feed material, with the feed mechanism 11 being relied instead on the tension springs 29. Accordingly, this prior art feed system 11 is reliant for automatic feed entirely upon the clamping force applied by the tension springs 29 for gripping the wood material fed to the gap 21, and the hydraulic cylinder comes into play only with manual input from the operator to either raise or lower the upper feed drum 15.
It is an object of the present invention to overcome the inherent limitations presented by the tension spring-type automatic feed mechanism for wood reducing apparatus while retaining the capability of manually raising the upper feed drum to accommodate the introduction of very large or awkward feed material to the gap between the feed drums.